Enhancement of Material Properties by Infiltration of Powder Metal Part:  Formulation and Method of Application Thereof

ABSTRACT

Infiltration compositions comprising chromium and at least about 80% copper. The infiltration compositions may further comprise iron, zinc, manganese, antimony and/or lubricants. Also, methods for infiltrating powder metal parts comprising contacting a powder metal part with the infiltration composition comprising chromium and at least about 80% copper and heating the powder metal part and infiltration composition to a temperature sufficient to melt the infiltration composition and allow the infiltration composition to infiltrate through pores in the powder metal part.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 60/883,192 filed on Jan. 3, 2007, which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns improvement in material properties of powder metal parts upon infiltrating with copper based formulations with addition of chromium and chromium based alloys. Metallographic studies indicate the homogeneity of distribution of copper-eutectoids throughout the interstices of iron-based powder metal parts. This method exhibits superior mechanical properties compared to the conventional infiltrating compounds and alloys available in any physical forms.

2. The Related Art

Enhancing the properties of powder metal parts produced by powder compression and sintering requires infiltration using a metal composition of melting point lower than that of the metal constitute powder metal parts. The compressed powder metal parts upon sintering leave a network of interconnecting void channels or capillaries. The process of infiltration using a metal composition that melts at a lower temperature than the powder metal parts allows the infiltrating material to percolate through the capillaries and fill in the voids resulting in the improvement of material properties of the powder metal parts. In general for powder metal parts comprising iron and its alloys, the infiltration compositions are typically based on copper.

The infiltration process involves placing the infiltration composition in contact with the powder metal parts, and then subjecting them to a temperature close to the melting point of the infiltrating composition under a reducing atmosphere in order to avoid the formation of metal oxides. Upon melting, the infiltrating material diffuses through the capillaries thereby forming microstructures throughout the interstices and strengthening the properties of the powder metal parts. The uniformity of distribution of infiltrated materials and the formation of microstructures there from brings about the enhancement of material properties.

The use of chromium in copper in the alloyed forms is known for enhancing material strength, corrosion resistance and electrical conductivity. Copper-chromium alloys are generally high copper solid solutions of chromium. These alloys undergo changes in properties due to the precipitation of chromium out of the solid solution as the temperature of the molten phase of the alloy cools down. The strength of fully aged chromium copper is nearly twice that of pure copper and its conductivity remains high at 85% IACS, or 85% that of pure copper. These high strength alloys retain their strength at elevated temperatures. The corrosion resistance of chromium copper alloys is better than that of pure copper because chromium improves the chemical properties of the protective oxide film. Chromium copper has excellent cold formability and good hot workability. It is used in applications such as resistance welding electrodes, seam welding wheels, switch gears, cable connectors, circuit breaker parts, molds, spot welding tips, and electrical and thermal conductors that require strength. Chromium copper alloys are designated as UNS C18050 through C18600, the cast alloys are C81400 through C81540.

All parts and percentages set forth in this specification are on a weight-by-weight basis, unless otherwise specified.

SUMMARY OF INVENTION

An aspect of the invention pertains to methods to improve material properties of iron based powder metal parts that involves infiltration that allows formation of unique uniform microstructures in the capillaries providing enhanced material strength. The infiltration composition comprises copper and copper alloys, and in an embodiment of the invention the total copper content in the composition is at least about 80%, by weight. The infiltration composition further comprises metallic chromium and its alloys which are used in the invention to achieve refined microstructures of metals in powder metal parts. In an embodiment of the invention, the chromium alloy has a chromium content of at least about 0.1%, by weight, or more. The infiltration composition, optionally, further comprises iron and/or manganese either in their individual metallic forms or in their alloyed forms. In an embodiment of the invention, the infiltration composition comprises at least about 0.1%, by weight of iron and/or manganese, respectively, preferably at most about 0.5% iron and/or manganese. In further embodiments, the infiltration composition comprises antimony. Depending upon the preferred forms of application, the infiltration composition further, optionally, comprises lubricants and in an embodiment, the amount of lubricant in the infiltration composition does not exceed more than 2%, by weight. The lubricant may be a fatty acid based lubricant.

Another aspect of the invention involves application of the infiltration composition in various physical forms, such as, compressed blocks (wafers, cylinders, bars etc.) prepared from the powder form of infiltration composition. The infiltration composition can also be applied in the form of pastes, such as those prepared from liquid or gelled petroleum oils and also from glycol ethers, long chain fatty alcohols and their combinations. The infiltration composition can also be applied in the form of extruded objects drawn from the powdered form of the infiltration composition. Thus, the invention concerns methods for enhancement of material properties of powder metal parts by infiltrating a composition which methods comprise the steps of providing the infiltration composition described herein, providing a powder metal part, contacting the infiltration composition to the powder metal part and heating the combined powder metal part and infiltration composition.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1A is a chart of the Rockwell Hardness (H Scale) versus the weight percent of chromium after infiltration of powder metal parts forms with infiltration compositions in accordance with embodiments of the invention.

FIG. 1B is a chart of the Rockwell Hardness (H Scale) versus the weight percent of antimony after infiltration of powder metal parts forms with infiltration compositions in accordance with embodiments of the invention.

FIG. 1C is a chart of the Transverse Rupture Strength (KSI) versus the weight percent of chromium after infiltration of powder metal parts forms with infiltration compositions in accordance with embodiments of the invention.

FIG. 2 is a set of scanning electron microscope (“SEM”) and energy dispersion X-ray technique (“EDX”) pictures of polished metallographic sections infiltrated (10% by weight of the powder metal part) by the comparative infiltration composition which does not comprise chromium.

FIG. 3A is a set of SEM and EDX pictures of polished metallographic sections infiltrated (10% by weight of the powder metal part) by an infiltration composition in accordance with embodiments of the invention (Example 2) comprising 0.3% chromium.

FIG. 3B is a set of SEM and EDX pictures of polished metallographic sections infiltrated (10% by weight of the powder metal part) by an infiltration composition in accordance with an embodiment of the invention (Example 2) comprising 0.6% chromium.

FIG. 4 is a chart of the Rockwell Hardness (H Scale) versus the weight percent of chromium of a wafer compacted with bonded powder in accordance with embodiments of the invention.

FIG. 4A is a set of SEM pictures showing chromium powder, copper powder, bonded copper and chromium powders showing adhered chromium particles on copper particles and blended copper and chromium powders showing random mixtures of both copper and chromium in accordance with embodiments of the invention.

FIG. 5 is a chart of the Rockwell Hardness (H Scale) versus the weight percent of chromium of a wafer compacted from a pre-alloyed blend in accordance with embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention concerns copper based infiltration compositions comprising (a) at least about 80% by weight copper, (b) about 0.1 to 3.5% by weight chromium, preferably about 0.5% to 3.5% by weight chromium, either in single metal or alloyed forms, (c) optionally about 0.1 to 3.5% by weight iron as single metal, or alloy, or metal complex forms, (d) optionally about 0 to 2.0% by weight of zinc either as single metal or alloyed forms, (e) optionally about 0 to 2% by weight of manganese either as single metal or alloyed forms and (f) optionally about 0 to 2% by weight of lubricants, such as those derived from organic fatty acids as their esters, amides, amine neutralized salts and their metal salts. Examples of lubricants include stearamides; alkali or alkaline metal salts; such as salts of lithium, sodium, potassium, ribidium, cesium, and francium; alkali or alkaline earth metal salts such as salts of beryllium; magnesium, calcium, strontium, barium and radium; transition metal salts and combinations thereof. Further, the invention concerns methods of enhancement of material properties of powder metal parts, i.e. improved powder metal parts and improvements to processes for making powder metal parts by infiltrating a composition of any conventional physical form, such as compressed blocks, or solid pastes, or extruded bars or cylinders. The invention also concerns methods for infiltrating a powder metal part and making powder metal parts comprising the steps of (i) providing copper based composition(s) with selective incorporation of chromium and chromium based alloy(s), comprising (a) at least about 80% by weight copper, (b) about 0.1 to 3.5%, preferably about 0.5% to 3.5%, by weight chromium either in single metal or alloyed forms, (c) optionally about 0.1 to 3.5% by weight iron as single metal, or alloy, or metal complex forms, (d) optionally about 0 to 2%, preferably about 0.1% to 2%, by weight of zinc, either as single metal or alloyed forms, (e) optionally about 0 to 2%, preferably about 0.1% to 2%, by weight of manganese either as single metal or alloyed forms and (f) optionally about 0 to 2%, preferably about 0.1% to 2%, by weight of lubricants, such as those derived from organic fatty acids as their esters, amides, amine neutralized salts and their metal salts, (ii) providing a powder metal part(s), (iii) contacting the infiltration composition to the powder metal part(s), and (iv) heating the combined powder metal part(s) and infiltration composition to a temperature enabling the infiltration composition to melt and infiltrate through the pores of powder metal part(s). The infiltration composition may be provided in one or more suitable forms, such as (a) compressed blocks of desired shapes and dimensions (conventionally known as ‘Slug’), (b) in the form of extruded bars, or cylinders, or hollow tubes of desired dimensions, (c) in the form of solid pastes compounded with gelled petroleum or other liquid organic binders derived from ethereal poly-alcohols, fatty alcohols, mineral oil, and combinations thereof, such as hydrocarbon resin (coumer) solutions in ketonic, alcoholic and hydrocarbon solvents, phenyl laurapel 81 and combinations thereof. In an embodiment of the invention the method comprises the temperature to operate infiltration of least about 800° C., such as from about 800° C. to about 1150° C.

In embodiments of the invention the infiltration composition may comprise at least about 90% by weight of copper. In further embodiments the infiltration composition comprises at least about 0.3%, by weight chromium, preferably at least about 0.6% chromium. In embodiments the infiltration composition comprises from about 0.1% to 2% chromium, such as about 0.1% to 0.6% chromium.

The chromium may be in powder form and also may be in alloyed form in combination with iron, manganese and copper and combinations thereof. In embodiments of the invention, the powdered form of chromium is bound with the infiltration composition by means of a binder, such as materials selected from the group consisting of hydrocarbon, acrylic, phenolic and combinations thereof. Examples of binders include polyglycol ether; alcohols typically octanol, hexadecanol, pentanol and/or dodecanol; hydrocarbon resin (coumer) solutions in ketonic, alcoholic and hydrocarbon solvents; and combinations thereof.

The infiltration composition may be in one of several physical forms. For example, the infiltration composition may be in the form of compressed powder (or slug). The infiltration composition may be in the form of paste, wherein the copper powder can be of either spherical or irregular or the combination of both, or the paste can be comprised of pre-alloyed copper powders of Cu—Zn, Cu—Sn, Cu—Cr, Cu—Ni, Cu—Mn, Cu—Sb, Cu—Pb, Cu—Bi, Cu—P, Cu—Al, and any combination of metals alone or their mixtures from the periodic table. The infiltration composition may be extruded as solid bar, cylinder, or hollow tube.

In the method, a powdered metal part based on iron may be sintered. In a further embodiment of the invention, the powder metal part is an iron based alloy and the infiltrated part has generally uniform distribution of copper eutectoids. In these embodiments of the invention, the powder metal part generally has a higher tensile strength compared to the compositions without chromium and may further have higher transverse rupture strength and higher yield strength.

Inclusion antimony may be used in an embodiment of the invention in conjunction with copper and chromium of the infiltration composition and applied in the methods of the present invention. The presence of antimony provides synergy to the effect of copper and chromium. The presence of antimony may also provide lubricity and ease of machining the metal parts. In embodiments of the invention, the amount of antimony may be about 0.01% to about 0.5%, preferably about 0.1% to about 0.5%.

The performances of the infiltration compositions of the invention are compared with conventional infiltration compositions. The formation of unique uniform micro structures is confirmed by metallographic studies by SEM and EDX, as shall be discussed below.

EXAMPLES Example 1 Comparative Preparation of Conventional Infiltration Composition

The conventional non-residue type infiltration composition was prepared by blending 97 weight (wt) % of Copper, 2 wt % of Iron, and 1 wt % of Zinc. The powder blend was further mixed with 0.5 wt % of Lithium (Li) stearate, or optionally a blend of Li-stearate and Stearamide waxes (commercially available as Acrawax). This blend was further converted in the following physical forms. Infiltration was carried out by placing one of the following infiltrant forms on the powder metal parts of dimension 1.25″×0.5″×0.25″ made by compressing iron based alloyed powders or premix of MPIF (Metal Powders Industrial Federation) standard (F-0008), which is incorporated by reference herein in its entirety. The powder metal part is compressed to a density 6.7 g/cc. The infiltrant forms used are 10 wt % of the powder metal parts.

(i) Compressed infiltrant wafer: The infiltration composition mixes of example 1, 10 wt % of the powder metal parts, was compressed in the form of rectangular wafer of density 7.5 g/cc. The compressed wafer was placed on the powder metal part and sintered together to allow infiltration to occur in a furnace of reducing atmosphere at 2050° F. (or 1121° C.). Then the infiltrated parts were cooled down to room temperature and the mechanical properties were tested.

(ii) Extruded infiltrant bar: By adopting Conform Extrusion technique of powders (U.S. Pat. No. 5,503,796, which is incorporated by reference herein in its entirety), the infiltration composition of Example 1 was extruded in the form of cylindrical rods of dimension 0.1″ in diameter. A length of the rod weighing 10 wt % of the powder metal part was placed and followed sintering-infiltration as in subpart (i) of this Example.

(iii) Infiltrant paste: The infiltration composition of Example 1 was pasted in petroleum jelly (and also alternately in alkylated glycolethers, mineral oils, higher fatty alcohols, for example dodecanol, hexadecanol etc.). Then a proportionate amount of the paste equivalent to 10 wt % of the powder metal part was spread on the object and subjected to sintering and infiltration as mentioned above. The comparative results are given in Table 1A.

Example 2 Preparation of the Infiltration Composition of the Invention

The infiltration composition of the invention was prepared by blending 92-97 weight (wt) % of Copper, and 0-4 wt % of Chromium, 2 wt % of Iron, and 1 wt % of Zinc. The composition with no chromium is a comparative example and the infiltrant compositions of the invention in the example contained from 0.3 to 3.5% chromium. The powder blends of different weight percent of chromium were further mixed with 0.5 wt % of Lithium (Li) stearate, or optionally a blend of Li-stearate and Stearamide waxes (commercially available as Acrawax). These blends were further converted in the following physical forms. Infiltrations were carried out by placing one of the following infiltrant forms on the powder metal parts of dimension 1.25″×0.5″×0.25″ made by compressing iron based alloyed powders as described in Example 1. The powder metal part is compressed to a density 6.7 g/cc. The infiltrant forms used are 10 wt % of the powder metal parts. These compositions were also studied with a small addition of antimony (0.1-0.5 wt %) for synergistic effects on the material strength. The results on the synergistic effects for the powder-metal parts infiltrated with a composition comprising antimony and chromium are given in Table 1B. The transverse rupture strengths of the infiltrated powder metal parts of the present invention are given in FIG. 1C.

(i) Compressed infiltrant wafer: The infiltration compositions mixes of Example 2, each consisting of 10 wt % of the powder metal parts, were compressed in the form of rectangular wafers of density 7.5 g/cc. The compressed wafer was placed on the powder metal part and sintered together to allow infiltration to occur in a furnace of reducing atmosphere at 2050° F. (or 1121° C.). Then the infiltrated parts were cooled down to room temperature and the mechanical properties were tested. The comparative results are given in Table 1A.

(ii) Extruded infiltrant bar: By adopting Conform Extrusion technique of powders (U.S. Pat. No. 5,503,796), the infiltration compositions of Example 2 were extruded in the form of cylindrical rods of dimension 0.1″ in diameter. For each of the compositions of Example 2, a length of the rod weighing 10 wt % of the powder metal part was placed and followed sintering-infiltration as in Subpart (i) of this Example. The comparative results are given in Table 1A.

(iii) Infiltrant paste: The infiltration compositions of Example 2 were pasted in petroleum jelly (and also alternately in alkylated glycol ethers, mineral oils, higher fatty alcohols, for example dodecanol, hexadecanol etc.). Then a proportionate amount of each of the pastes of the compositions of Example 2, equivalent to 10 wt % of the powder metal part, was spread on the object and subjected to sintering and infiltration as mentioned above. The comparative results are given in Table 1A.

The plot of Rockwell hardness versus percentage of chromium in the infiltration composition for the various forms of powder metal parts comprising the infiltration composition forms of Example 2 is shown in FIG. 1A. The plots on the synergistic effect caused by the addition of antimony to the infiltration compositions of Example 2 are shown in FIG. 1B. The plot of transverse rupture strengths of the infiltrated powder metal parts of Example 2 at various percentages of chromium is shown in FIG. 1C.

Example 3 Metallographic Studies on the Infiltration Compositions

The microstructures of the infiltrated powder metal parts of Examples 1 and 2 were further studied and compared by metallography. The specimens of the excised sections of the infiltrated powder metal parts were polished and etched using 2% Nital solution (ethanolic solution of nitric acid). All of the polished and etched specimens of the infiltrated parts were examined by SEM (scanning electron microscope) at various magnifications followed by EDX (energy dispersion x-ray technique). The polished and etched transverse rupture sections were placed within the chamber of a scanning electron microscope under vacuum. Each sample was subjected to X-rays to provide an image of the surface of the sample and to get the profiles of microstructures of elemental or eutectoid forms of metal compositions. This was accomplished using an auxiliary energy dispersive cell to obtain the surface topography and maps of the constituents within the microstructures of the infiltrated specimens. The EDX pictures of the infiltrated locations of the powder metal interstices enriched by the microstructures of copper-chromium eutectoids are shown in FIGS. 2, 3A and 3B.

FIG. 2 includes a SEM picture 1 of a specimen that comprises an infiltration composition that does not contain chromium. In EDX photograph 2, the infiltration composition does not contain copper and this EDX photograph shows profiles of an iron-rich location, i.e., an iron map. EDX photograph 3 shows a copper map for a composition that does not comprise chromium showing copper-rich locations 4 (brighter sections) within the powder metal part.

FIG. 3A includes a SEM picture 5 of a specimen that comprises an infiltration composition having 0.3% chromium. EDX photograph 6 is an iron map which shows the iron-rich locations of the specimen comprising an infiltration composition having 0.3% chromium. EDX photograph 7 shows a copper map for the specimen comprising 0.3% chromium showing copper-rich locations 8 (brighter sections) within the powder metal part.

FIG. 3B includes a SEM picture 9 of a specimen that comprises an infiltration composition having 0.6% chromium. EDX photograph 10 is an iron map which shows the iron-rich locations of a specimen comprising an infiltration composition having 0.6% chromium. EDX photograph 11 shows a copper map for a specimen comprising 0.6% chromium showing copper-rich locations 12 (brighter sections) within the powder metal part.

The respective microstructures and the location of their constituents in samples with and without chromium revealed the differences. For example, FIG. 3B shows the evidence of copper microstructures resulting from the formation of eutectoids in the presence of chromium, whereas the FIG. 2 (which did not contain chromium) showed poor reaction of copper within the interstices of iron particles.

Example 4 Preparation of the Infiltration Composition of the Invention Using Bonded Copper-Chromium Granules

In this example, the copper and chromium powders were pre-bonded using low molecular weight poly methyl methacrylate, condensation polymers of oleic acid and acrylic acid, and hydrocarbon resin (coumer) solutions in ketonic, alcoholic and hydrocarbon solvents. The polymeric binders used as 5-10% solutions in either of those solvents. Copper and chromium powders having the amounts of copper and chromium of Example 2 were blended with 5% (wt) of the polymer solutions described above in a rotary tumbler. Upon blending, the organic solvent was removed from the blend by drying. These dried bonded powder(s) of copper and chromium were then mixed with the remaining portion of other components like iron, zinc, and lubricant in the amounts and as described in Example 2. The purpose of pre-bonding copper and chromium powders was to prevent the possibility of segregation and to provide more intimacy to perform while transiting through the eutectic phase of the melt during infiltration process. The results of mechanical properties of the powder metal parts of this example after infiltration are given in Table 2 and a chart (FIG. 4) showing the Rockwell Hardness as a function of the amount of chromium in the infiltration composition. FIG. 4A is a series of SEM pictures of blended copper-chromium powders versus bonded copper-chromium powders of the invention which reveal the intimately adhered particle boundaries of copper-chromium. In FIG. 4A, photograph 13 shows chromium powder, photograph 14 shows copper powder, photograph 15 shows bonded copper and chromium powders with adhered chromium particles on the copper particles and photograph 16 shows blended copper and chromium powders with random mixtures of both copper and chromium.

Example 5 Preparation of the Infiltration Composition of the Invention Using Copper and Copper-Chromium Alloy Powder

The preparation of infiltration composition of the invention was followed according to the Example 4, wherein the chromium was incorporated to the formulation by means of using high-copper and chromium alloy UNS C18200. The formulation comprising copper powder and powdered form of UNS C18200 were present as 37-40 wt % of copper powder, 55-60 wt % of the powdered form of copper-chromium alloy of grade UNS C18200, 2 wt % of Iron, and 1 wt % of Zinc. The powder blends were further mixed with 0.5 wt % of Lithium (Li) stearate, or optionally a blend of Li-stearate and Stearamide waxes (commercially available as Acrawax). Infiltration experiments were carried out as per the method described in Example 2. The results of mechanical properties of the metal powder parts upon infiltration, i.e. Rockwell Hardness v. weight percent of chromium, are shown in Table 3 and FIG. 5.

TABLE 1A Wafer from compacted Wt. % of powder Extruded by Infiltrant paste Chromium as Rockwell conform process Rockwell in Examples Hardness Rockwell Hardness Hardness 1 and 2 (H scale) (H scale) (H scale) 0 88 88 88 0.3 98 98.5 97 0.6 100 100.5 98 1 100 100 98 2 98 98 97 3.5 95 94.5 93

TABLE 1B Wafer from Extruded by compacted conform Wt. % of Wt. % of powder process Chromium Antimony Rockwell Rockwell Infiltrant Paste as in as in Hardness Hardness Rockwell Hardness Example 2 Example 2 (H scale) (H scale) (H scale) 0.3 0 98 98.5 97 0.3 0.1 99 99 98 0.3 0.2 101 101.5 99 0.3 0.3 103 102 97.5 0.3 0.5 98.5 98 96

TABLE 2 Wafer from compacted powder of Example 4 Wt. % of Chromium Rockwell Hardness in Example 2 (H scale) 0 88 0.3 96 0.6 103 1 102 2 98 3.5 96

TABLE 3 Wafer from compacted powder of example 5 Wt. % of Chromium Rockwell Hardness in Example 1 (H scale) 0 88 0.3 98 0.6 99 1 101 2 95 3.5 94

Example 6

Copper infiltration of iron parts was carried out with F-0008 and FY-4500 iron powders based on the standards in powder metallurgy as described in the Material Standard for PM Structural Parts, MPIF Standard 35 which is incorporated herein by reference in its entirety (see, for example pages 36 and 56, 2000 Edition, Published by Metal Powders Industries Federation). The general properties and characteristics of the F-0008 and FY-4500 iron powders studied in this example are set forth in Table 4. The iron parts were compressed at various densities ranging between 6.7 g/cm³ to 7.2 g/cm³. Infiltration of the iron parts were verified using the infiltration composition of Example 2 and a conventional infiltrant system, as described in Example 1. The results (Table 5 and 6) showed improved performance of mechanical properties for the infiltration composition of the invention. The consistency in dimensional changes with the infiltration composition of the invention is evident at various densities of the iron parts studied.

TABLE 4 Properties F-0008 FY-4500 AD, g/cm³ 3.16 3.11 Hall Flow, s/50 g 39 28.7 Green Strength, psi 1500 1930 Compressibility at 6.8 6.8 30tsi, g/cm³ Lube, % 1 0.75 Transverse Rupture 101 107 Strength, 10³ psi

TABLE 5 Comparison of mechanical properties of the sintered parts using iron powder F-0008 by conventional method of infiltration (A) as well as the method of the invention (B). Transverse Rockwell Dimensional Sintered Green Strength Hardness Change Density Density (× 1000 PSI) (B Scale) (%) (g/cc) (g/cc) A B A B A B A B 6.7 160.10 167.10 82.10 84.00 0.70 0.69 7.15 7.18 7 185.20 198.64 85.10 89.60 0.83 0.70 7.47 7.57 7.2 204.20 229.50 88.40 94.20 0.90 0.69 7.61 7.71 A: Conventional Infiltrating system as described in Example-1 [section (i)] B: Method of present invention as described in Example-2 [Section (ii)]

TABLE 6 Comparison of mechanical properties of the sintered parts using iron powder FY-4500 by conventional method of infiltration (A) as well as the method of the invention (B). Transverse Rockwell Dimensional Sintered Green Strength Hardness Change Density Density (× 1000 PSI) (B Scale) (%) (g/cc) (g/cc) A B A B A B A B 6.7 162 171 82.7 85.8 0.80 0.78 7.21 7.27 7 196 201 88.3 91.2 0.87 0.80 7.42 7.53 7.2 207 214 91.7 94.0 0.98 0.90 7.64 7.67 A: Conventional infiltrating system as described in Example-1 [section (i)] B: Method of present invention as described in Example-2 [Section (ii)]

Example 7 Helical Gear

A standard iron gear part, a helical gear, was selected to test and compare the performance of an infiltration system in accordance with the invention versus a conventional system. The iron helical gears, compacted to a green density of 6.7 g/cc were infiltrated with an infiltration composition in accordance with the invention [Example 2; Section (ii)], a conventional infiltrant system [Example 1; Section (i)] and without infiltrant. The gear was compressed from the iron powder grade F-0008 (Table 4). The surface hardness of the infiltrated parts was measured using the Rockwell Hardness Tester. The results are given in Table 7 showing improvement in surface hardness. The amount of infiltration composition is about twelve weight percent of the base iron part.

Further, the infiltrant system of the invention [Example 2, Section (ii)] resulted in helical gear having a clean and smooth surface finishing compared to the helical gear prepared with conventional infiltration compositions and systems. The powder metal part prepared with the convention infiltration composition and system had a rough surface after the process. Without being bound to any theory, the inventors believe that the rough surface on the part prepared with conventional infiltration compositions resulted from traces of infiltrant residue on the surface of the powder metal part because the infiltration composition did not completely infiltrate the surface of the part thus causing imperfect infiltration.

Cylindrical Bushing

An iron cylindrical bushing was also selected to measure the performance of the infiltration system of the invention. The cylindrical shape limits the contact area between the base part, i.e. the cylindrical bushing, and the infiltrant system. Because of this, conventional infiltration compositions and systems tend to show poor surface finishing, traces of sooty residues and dimensional instability. The cylindrical bushings prepared for this example were compacted to a green density of 6.7 g/cc and infiltrated with the infiltration composition and system of the invention [Example 2; Section (ii)], with a conventional infiltrant system [Example 1; Section (i)] and without incorporating any infiltrant. The bushings were made from the iron powder grade of FY-4500. The surface hardness of the infiltrated parts was measured using the Rockwell Hardness Tester. The results are given in Table 7 showing improvement in surface hardness for the metal part prepared in accordance with the invention. Also, the cylindrical bushing prepared in this example with the infiltration composition and system of the invention had a clean and smooth surface finishing whereas the part prepared with the conventional system had a surface with an undesired sooty appearance. The amount of infiltrant used in all experiments was approximately twelve weight percent of the base iron part.

TABLE 7 Surface hardness comparison of the infiltration system of the invention versus conventional iron powdered metal parts. Rockwell Hardness (B Scale) A B C Helical 85 93 60 Gear Cylindrical 85 92 51 Bushing A: Conventional infiltrating system as described in Example-1 [section (i)] B: Infiltration composition and method of invention as described in Example-2 [Section (ii)] C: As sintered iron powder metal part (without any infiltration) 

1. An infiltration composition comprising at least about 80% copper and chromium.
 2. The infiltration composition of claim 1 further comprising at least about 0.5% iron or at least about 0.5% manganese.
 3. The infiltration composition of claim 1 comprising about 0.1% to about 3.5% chromium.
 4. The infiltration composition of claim 3 comprising about 0.1% to about 3.5% iron, up to about 0.2% zinc, up to about 0.2% manganese and up to about 0.2% lubricants.
 5. The infiltration composition of claim 4 wherein the lubricant is fatty acid based.
 6. The infiltration composition of claim 1 comprising at least about 90% by weight copper.
 7. The infiltration composition of claim 1 further comprising antimony.
 8. The infiltration composition of claim 7 comprising about 0.01% to about 0.5% antimony.
 9. The infiltration composition of claim 1 wherein the chromium is part of an alloy with a metal selected from the group consisting of iron, manganese, copper and combinations thereof.
 10. The infiltration composition of claim 1 wherein chromium powder is bound to the infiltration composition by a binder selected from the group consisting of hydrocarbon binder, acrylic binder, phenolic binder and combinations thereof.
 11. The infiltration composition of claim 1 in the form of a paste.
 12. The infiltration composition of claim 11 wherein the copper is in the form of a spherical powder, irregular powder or combinations thereof.
 13. The infiltration composition of claim 11 wherein the paste comprises pre-alloyed copper powders of Cu—Zn, Cu—Sn, Cu—Cr, Cu—Ni, Cu—Mn, Cu—Sb, Cu—Pb, Cu—Bi, Cu—P, Cu—Al and combinations thereof.
 14. The infiltration composition of claim 11 wherein the paste further comprises a material selected from the group consisting of gelled petroleum, ethereal poly-alcohols, fatty alcohols, mineral oil and combinations thereof.
 15. A powder metal part comprising the infiltration composition of claim
 1. 16. A method for infiltrating a powder metal part with an infiltration composition comprising the steps of providing an infiltration composition comprising at least about 80% copper and chromium, providing the powder metal part, contacting powder metal part with the infiltration composition and heating the powder metal part while the powder metal part is in contact with the infiltration composition to a temperature that allows the infiltration composition to melt and infiltrate through pores in the powder metal part.
 17. The method of claim 16 wherein the infiltration composition comprises at least about 0.1% by weight chromium.
 18. The method of claim 17 wherein the infiltration composition comprises about 0.5% to 3.5% by weight chromium, about 0.1% to 3.5% by weight iron, up to about 2.0% by weight of zinc, up to about 2% by weight of manganese and up to about 2% by weight of lubricants.
 19. The method of claim 18 wherein the lubricant is fatty acid based.
 20. The method of claim 16 wherein the infiltration composition comprises at least about 90% copper.
 21. The method of claim 16 wherein the infiltration composition further comprises antimony.
 22. The method of claim 21 wherein the antimony is used in amounts of about 0.01% to about 0.5%.
 23. The method of claim 16 wherein the infiltration composition is in a form selected from the group consisting of compressed blocks, extruded bars, extruded cylinders, extruded hollow tubes and solid pastes.
 24. The method of claim 16 wherein the solid pastes are compounded with a material selected from the group consisting of gelled petroleum, ethereal poly-alcohols, fatty alcohols, mineral oil and combinations thereof.
 25. The method of claim 16 wherein the temperature is at least about 800° C. 